testCategory property for gradle test tasks

[Sai Boorlagadda <sa...@apache.org>]

All,

I merged a commit to 'develop' to remove all sub-category testing tasks
like dlockTest,clientSubscriptionTest etc. After we moved integration &
distributed tests to respective folders these tasks are running
against only unit test source. Added a new property 'testCategory' to run
specific category tests instead of a task for every sub-category and
test-type combination.

Here's how you can run a specific category test with new changes:

./gradlew -PtestCategory=org.apache.geode.test.junit.categories.GfshTest
distributedTest

This allows developers to choose a specific test category and target a test
source.

Sai